Apparatus and method to store information in a holographic data storage medium

ABSTRACT

A method to store information in a holographic data storage medium, wherein the method supplies a holographic data storage medium comprising an encoded focusing hologram and one or more encoded data holograms. The method disposes the holographic data storage medium in a holographic data storage system, and disposes a rotatable imaging lens at an (i)th orientation. The method illuminates the encoded focusing hologram to generate an (i)th reconstructed focusing image, projects that (i)th reconstructed focusing image through the rotatable imaging lens, and onto at optical detector array. The method then calculates an (i)th measured focusing metric, and determines if the (i)th measured focusing metric is greater than or equal to the threshold focusing metric. If the (i)th measured focusing metric is greater than or equal to the threshold focusing metric, then the method decodes the one or more encoded data holograms.

FIELD OF THE INVENTION

This invention relates to an apparatus and method to store informationin a holographic data storage medium.

BACKGROUND OF THE INVENTION

In holographic information storage, an entire page of information isstored at once as an optical interference pattern within a thick,photosensitive optical material. This is done by intersecting twocoherent laser beams within the storage material. The first, called thedata beam, contains the information to be stored; the second, called thereference beam, is designed to be simple to reproduce, for example asimple collimated beam with a planar wavefront.

The resulting optical interference pattern causes chemical and/orphysical changes in the photosensitive medium: a replica of theinterference pattern is stored as a change in the absorption, refractiveindex, or thickness of the photosensitive medium. When the storedinterference pattern is illuminated with one of the two waves that wereused during recording, some of this incident light is diffracted by thestored interference pattern in such a fashion that the other wave isreconstructed. Illuminating the stored interference pattern with thereference wave reconstructs the data beam, and vice versa.

A large number of these interference patterns can be superimposed in thesame thick piece of media and can be accessed independently, as long asthey are distinguishable by the direction or the spacing of thepatterns. Such separation can be accomplished by changing the anglebetween the object and reference wave or by changing the laserwavelength. Any particular data page can then be read out independentlyby illuminating the stored patterns with the reference wave that wasused to store that page. Because of the thickness of the hologram, thisreference wave is diffracted by the interference patterns in such afashion that only the desired object beam is significantly reconstructedand imaged on an electronic camera. The theoretical limits for thestorage density of this technique are on the order of tens of terabitsper cubic centimeter.

SUMMARY OF THE INVENTION

Applicants' invention comprises a method to store information in aholographic data storage medium. The method supplies a holographic datastorage medium comprising an encoded focusing hologram and one or moreencoded data holograms, and provides a first holographic data storagesystem comprising a light source, an optical detector array and arotatable imaging lens.

The method disposes the holographic data storage medium in theholographic data storage system, and disposes the rotatable imaging lensat an (i)th orientation. The method illuminates the encoded focusinghologram with a reference beam to generate an (i)th reconstructedfocusing image, projects that (i)th reconstructed focusing image throughthe rotatable imaging lens, and onto the optical detector array. Themethod then calculates an (i)th measured focusing metric, and determinesif the (i)th measured focusing metric is greater than or equal to thethreshold focusing metric. If the method determines that the (i)thmeasured focusing metric is greater than or equal to the thresholdfocusing metric, then the method decodes the one or more encoded dataholograms.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from a reading of the followingdetailed description taken in conjunction with the drawings in whichlike reference designators are used to designate like elements, and inwhich:

FIG. 1A is perspective view of a holographic data storage medium;

FIG. 1B is a cross-sectional view of the holographic data storage mediumof FIG. 1A;

FIG. 2A is a perspective view of a one embodiment of a holographic datastorage system shown encoding information into the holographic datastorage medium of FIGS. 1A and 1B;

FIG. 2B shows a focusing lens element of the system of FIG. 2A, whereinthat focusing lens introduced one or more optical aberrations into theimage encoded;

FIG. 3A is a perspective view of a second embodiment of a holographicdata storage system shown encoding information into the holographic datastorage medium of FIGS. 1A and 1B;

FIG. 3B shows a focusing lens element of the system of FIG. 2A, whereinthat focusing lens introduced one or more optical aberrations into theimage encoded;

FIG. 4 is a block diagram showing the holographic data storage system ofFIG. 3;

FIG. 5 is a perspective view of a one embodiment of a holographic datastorage system shown decoding information encoded into the holographicdata storage medium of FIGS. 1A and 1B;

FIG. 6 is a perspective view of a second embodiment of a holographicdata storage system shown decoding information encoded into theholographic data storage medium of FIGS. 1A and 1B;

FIG. 7 is a block diagram showing one embodiment of Applicants'holographic data storage system;

FIG. 8 shows a rotatable imaging lens assembly used to direct aprojected image onto an optical detector array;

FIG. 9 shows one embodiment of the rotatable imaging lens assembly ofFIG. 8;

FIG. 10 shows one embodiment of Applicants' focusing image;

FIG. 11 shows a second embodiment of Applicants' focusing image;

FIG. 12 is a flow chart summarizing certain steps of Applicants' methodto store information in a holographic data storage medium;

FIG. 13 is a flow chart summarizing the steps of Applicants' method tostore information in a holographic data storage medium;

FIG. 14 is a flow chart summarizing certain addition steps ofApplicants' method to store information in a holographic data storagemedium; and

FIG. 15 is a flow chart summarizing certain addition steps ofApplicants' method to store information in a holographic data storagemedium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention is described in preferred embodiments in the followingdescription with reference to the Figures, in which like numbersrepresent the same or similar elements. Reference throughout thisspecification to “one embodiment,” “an embodiment,” or similar languagemeans that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the present invention. Thus, appearances of the phrases “in oneembodiment,” “in an embodiment,” and similar language throughout thisspecification may, but do not necessarily, all refer to the sameembodiment.

The described features, structures, or characteristics of the inventionmay be combined in any suitable manner in one or more embodiments. Inthe following description, numerous specific details are recited toprovide a thorough understanding of embodiments of the invention. Oneskilled in the relevant art will recognize, however, that the inventionmay be practiced without one or more of the specific details, or withother methods, components, materials, and so forth. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the invention.

Referring now to FIGS. 2A and 2B, holographic data storage system 200comprises lasing device 205, a beam splitter 210, transmissive SpatialLight Modulator (“SLM”) 215 and mirror 280. In certain embodiments,lasing device 205 emits blue light at a wavelength of about 405 nm. Incertain embodiments, lasing device 205 emits or red light at awavelength of about 650 nm. In certain embodiments, lasing device 205emits or infrared light at a wavelength of about 780 nm. In certainembodiments, lasing device 205 emits other wavelength(s) of light tunedto the recording and/or reading characteristics of holographic datastorage medium 100 (FIGS. 1A, 1B).

In certain embodiments, transmissive SLM 215 comprises an LCD-typedevice. Information is represented by either a light or a dark pixel onthe SLM 215 display. The SLM 215 is typically translucent.

Laser light originating from the lasing device 205 is split by the beamsplitter 210 into two beams, a carrier beam 220 and a reference beam230. The carrier beam 220 picks up the image 240 displayed by the SLM215 as the light passes through the SLM 215 to form data beam 260. Databeam 260 passes through focusing lens 250 as focused data beam 265. Incertain embodiments, focused data beam 265 comprises one or more opticalaberrations 255. Reflected reference beam 290 interferes with focuseddata beam 265 to form a hologram, which is encoded into holographicstorage medium 100 as interference pattern 270.

In certain embodiments, image 240 comprises a focusing image. In certainembodiments, image 240 comprises focusing image 1000 (FIG. 10), andinterference pattern 270 encodes that focusing image 1000 intoholographic data storage medium 100. In certain embodiments, image 240comprises focusing image 1100 (FIG. 11), and interference pattern 270encodes that focusing image 1100 into holographic data storage medium100. In certain embodiments, image 240 comprises a data image, andinterference pattern 270 encodes that data image into holographic datastorage medium 100.

Referring now to FIGS. 3A, 3B, and 4, holographic data storage system300 comprises lasing device 205, beam splitter 210, reflective spatiallight modulator 310, focusing lens 350, and holographic storage medium100. The light generated by lasing device 205 is split by beam splitter210 into reference beam 320, and carrier beam 330.

In the illustrated embodiment of FIGS. 3A, 3B, and 4, reflective spatiallight modulator (“RSLM”) 310 displays image 240. In certain embodiments,reflective spatial light modulator 310 comprises an assembly comprisinga plurality of micro-mirrors. In other embodiments, reflective spatiallight modulator 310 comprises a liquid crystal on silicon (“LCOS”)display device. In contrast to nematic twisted liquid crystals used inLCDs, in which the crystals and electrodes are sandwiched betweenpolarized glass plates, LCOS devices have the liquid crystals coatedover the surface of a silicon chip. The electronic circuits that drivethe formation of the image are etched into the chip, which is coatedwith a reflective (aluminized) surface. The polarizers are located inthe light path both before and after the light bounces off the chip.LCOS devices are easier to manufacture than conventional LCD displays.LCOS devices have higher resolution because several million pixels canbe etched onto one chip. LCOS devices can be much smaller thanconventional LCD displays.

Carrier beam 330 picks up image 240 as the light is reflected offreflective spatial light modulator 310 to form data beam 340 comprisingimage 240. Data beam 340 passes through focusing lens 350 as focuseddata beam 345. Unreflected reference beam 320 interferes with focuseddata beam 345 to form a hologram, which is encoded into holographic datastorage medium 100 as interference pattern 270. In certain embodiments,focused data beam 345 comprises one or more optical aberrations 355.

FIG. 5 illustrates holographic data storage system 200 decodinginterference pattern 270. In the illustrated embodiment of FIG. 5,holographic data storage system 200 further comprises translatablefocusing lens 810, rotatable imaging lens 850, and optical sensor array510. Optical sensor array 510 is disposed a distance away fromholographic storage medium 100 sufficient to digitally detect thefocused, astigmatism-reduced, reconstructed data beam 570 projected uponit.

To decode interference pattern 270, reference beam 230 is reflected offmirror 280, to form reflected reference beam 290, which is then incidenton the encoded holographic storage medium 100. As the reference beam 290interferes with interference pattern 270, a reconstructed data beam 550is generated, wherein that reconstructed data beam 550 comprises animage resembling the original image 240.

Reconstructed data beam 550 passes through translatable focusing lens810 as focused, reconstructed data beam 560. Focused, reconstructed databeam 560 passes through rotatable imaging lens 850 as focused,astigmatism-reduced, reconstructed data beam 570. That focused,astigmatism-reduced, reconstructed data beam 570 is projected ontooptical sensor array 510, which digitally detects the informationcomprising the projected image.

As those skilled in the art will appreciate, an astigmatism results froma defect in an optical system, wherein light rays from a single pointfail to converge in a single focal point. Such an astigmatism mayresults from an unequal curvature in a lens, such as focusing lens 250(FIGS. 2A, 2B), and/or focusing lens 350 (FIGS. 3A, 3B, 4), and/ortranslatable focusing lens 810 (FIGS. 5, 6).

Reconstructed data beam 550, translatable focusing lens 810, rotatableimaging lens 850, and optical sensor array 510, may be disposed on thesame side of holographic data storage medium 100 as are lasing device205 and mirror 280, if holographic data storage medium 100 isreflective. However, translatable focusing lens 810, rotatable imaginglens 850, and optical sensor array 510, may be disposed on the oppositeside of holographic data storage medium 100 as are lasing device 205 andmirror 280, if holographic data storage medium 100 is transmissive.

FIG. 6 shows holographic data storage system 300 being used to decodeinterference pattern 270. In the illustrated embodiment of FIG. 6,reference beam 320 is directed toward holographic storage medium 100such that reference beam 320 is diffracted by the interference pattern270 to form reconstructed data beam 650 comprising an image whichresembles the original image 240. Reconstructed data beam 650 passesthrough translatable focusing lens 810 as focused, reconstructed databeam 660. Focused, reconstructed data beam 660 passes through rotatableimaging lens 850 as focused, astigmatism-reduced, reconstructed databeam 670. That focused, astigmatism-reduced, reconstructed data beam 670is projected onto optical sensor array 510, which digitally detects theinformation comprising the projected image.

Translatable focusing lens 810, rotatable imaging lens 850, and opticalsensor array 510, may be disposed on the same side of holographic datastorage medium 100 as are lasing device 205 and mirror 280, ifholographic data storage medium 100 is reflective. However, translatablefocusing lens 810, rotatable imaging lens 850, and optical sensor array510, may be disposed on the opposite side of holographic data storagemedium 100 as are lasing device 205 and mirror 280, if holographic datastorage medium 100 is transmissive.

FIG. 7 illustrates one embodiment of Applicants' storage controller 760.In the illustrated embodiment of FIG. 7, computing devices 710, 720, and730 communicate with storage controller 760 through a data communicationfabric 740. In certain embodiments, fabric 740 comprises one or moredata switches 750. Further in the illustrated embodiment of FIG. 7,storage controller 760 communicates with one or more holographic datastorage systems. In the illustrated embodiment of FIG. 7, data storageand retrieval system 700 comprises holographic data storage systems 200and 300.

In certain embodiments, computing devices 710, 720, and 730, areselected from the group consisting of an application server, a webserver, a workstation, a host computer, or other like device from whichinformation is likely to originate. In certain embodiments, one or moreof computing devices 710, 720, and/or 730 are interconnected with fabric740 using Small Computer Systems Interface (“SCSI”) protocol runningover a Fibre Channel (“FC”) physical layer. In other embodiments, theconnections between computing devices 710, 720, and 730, comprise otherprotocols, such as Infiniband, Ethernet, or Internet SCSI (“iSCSI”). Incertain embodiments, switches 750 are configured to route traffic fromthe computing devices 710, 720, and/or 730, directly to the storagecontroller 760.

In the illustrated embodiment of FIG. 7, storage controller 760comprises a data controller 762, memory 763, microcode 822, processor764, and data caches 766, 767, and 768, wherein these componentscommunicate through a data bus 765. In certain embodiments, memory 763comprises a magnetic information storage medium, an optical informationstorage medium, an electronic information storage medium, and the like.By “electronic storage media,” Applicants mean, for example, a devicesuch as a PROM, EPROM, EEPROM, Flash PROM, COMPACTFLASH, SMARTMEDIA, andthe like.

In certain embodiments, the storage controller 760 is configured to readdata signals from and write data signals to a serial data bus on one ormore of the computing devices 710, 720, and/or 730. Alternatively, inother embodiments the storage controller 760 is configured to read datasignals from and write data signals to one or more of the computingdevices 710, 720, and/or 730, through the data bus 765 and the fabric740.

In certain embodiments, storage controller 760 converts a serial datastream into a convolution encoded data images. Those data images aretransferred to an SLM 215 or a RSLM 310.

In certain embodiments, the interconnected holographic data storagesystems 200, and 300, are located in different geographical places. Incertain embodiments, storage controller 760 distributes informationbetween two or more holographic data storage systems in order to protectthe information.

Referring now to FIGS. 8 and 9, translatable focusing lens 810 ismoveably disposed on solenoid assembly 820. Solenoid assembly 820 is incommunications with storage controller 760 via communication link 830.Communication link 830 (FIG. 8) is represented in FIG. 7 as 830 a forholographic data storage system 200 and as 830 b for holographic datastorage system 300.

The operation of translatable focusing lens 810 is described in theapplication having Ser. No. 11/682,206, which is assigned to the commonassignee hereof, and which is hereby incorporated herein by reference.

Rotatable imaging lens 850 is rotatably interconnected with servoassembly 840. In the illustrated embodiment of FIG. 8, optical sensorarray 510 is in communication with storage controller 760 viacommunication link 770 and/or 780 of FIGS. 7 and 8, and servo assembly840 is in communication with storage controller 760 via communicationlink 835. Communication link 835 (FIG. 8) is represented in FIG. 7 as835 a for holographic data storage system 200 and as 835 b forholographic data storage system 300.

In the illustrated embodiment of FIG. 9, servo assembly 840 comprisesservo 910 and rotatable shaft 920 extending outwardly therefrom.Rotatable shaft 920 can be positioned to specific angular orientationsby sending servo 910 a pre-defined coded signal. As long as that codedsignal exists on input line 835, servo 910 will maintain the associatedangular orientation of shaft 920. As the coded signal changes, theangular orientation of the shaft 920 changes.

In the illustrated embodiment of FIG. 9, rotatable shaft 920 comprisesspiral-threaded portion 930, and rotatable imaging lens 850 comprisesperiphery 940 and a plurality of gear teeth 950 disposed along periphery940. One or more of gear teeth 950 are intermeshed with threaded portion930 of rotatable shaft 920.

FIGS. 1A and 1B show holographic data storage medium 100 which rotatesabout center 105 about the Z-axis. In the illustrated embodiment of FIG.1B, holographic data storage medium 100 comprisesfactory-written-focusing-hologram 120 (FIG. 1B),drive-written-focusing-hologram 110 (FIG. 1B),computer-generated-focusing hologram 140 (FIG. 1B), and data hologram130 (FIG. 1B), wherein holograms 110, 120, 130, and 140, are eachencoded along data plane 150, which itself is sandwiched betweensubstrate 104 and cover 102.

Factory-written-focusing-hologram 120 (FIG. 1B) andcomputer-generated-focusing hologram 140 (FIG. 1B) are disposed withinthe holographic data storage medium by the media manufacturer at thetime of manufacture. By “at the time of manufacture,” Applicants meanprior to offering the holographic data storage medium for sale, andbefore encoding any information, such as for example customer data,therein.

In certain embodiments, computer-generated-focusing hologram 140 (FIG.1B) is stored on a read-only piece of media, which is then physicallyimplanted in the data plane 150 during a separate step of the overallmedia manufacturing process. In other embodiments, acomputer-generated-focusing hologram 140 is stamped or lithographed ontoholographic data storage medium 100 on data plane 150, as a separatestep of the overall media manufacturing process.

Factory-written-focusing-hologram 120 (FIG. 1B) is encoded directly intoholographic data storage medium 100 at the time of manufacture.Factory-written-focusing-hologram 120 (FIG. 1B) and/or the computergenerated-hologram 140 (FIG. 1B) are based on ranges of opticaltolerances. For the encoding holographic drive apparatus, such opticaltolerances include the refractive indices of all focusing lenses,refractive index of spatial light modulator (if a transmissive SLM isused), and refractive index of the beam splitter. For the media, theseoptical tolerances include the thicknesses and refractive indices ofeach layer of the holographic data storage medium.

In certain embodiments, Applicants' computer generated focusing hologramis formed using a bit stream suitable for use in a laser writer, such assimilar to a DVD-ROM master writer, for producing a stamped or writtencalibration hologram. In certain embodiments, the master comprises atwo-dimensional interference pattern for use in a photolithographic orlithographic-immersion stepper tool to produce a specific pattern. Incertain embodiments, the master comprises a three-dimensionalinterference pattern for use in a holographic imaging writer.

Data hologram 130 (FIG. 1B) is encoded into the holographic data storagemedium after purchase by the user. The apparatus used to encode a datahologram 130 may not comprise the same apparatus later used to decodethat data hologram 130 (FIG. 1B). Using a first apparatus to encode adata hologram, and a second apparatus to decode that hologram, is calledinterchange. In certain embodiments, one or moredrive-written-focusing-holograms 110 are encoded along with one or moredata holograms 130 (FIG. 1B). Those one or moredrive-written-focusing-holograms 110 are used to position translatablefocusing lens 810 (FIGS. 5, 6, 8), and/or rotatable imaging lens 850(FIGS. 5, 6, 8, 9) with respect to an encoded holographic data storagemedium and/or optical detector array 510 (FIGS. 5, 6, 8) when decodingone or more data holograms 130 (FIG. 1B).

Applicants' invention includes a method to decode one or more dataholograms, such as data hologram 130 (FIG. 1B), written to a holographicdata storage medium, such as holographic data storage medium 100,wherein that holographic data storage medium comprises an encodedfocusing image. References herein to an “encoded focusing image” mean aninterference pattern disposed in a holographic data storage medium,wherein that interference pattern encodes a focusing image, such as forexample and without limitation focusing image 1000 (FIG. 10) and/orfocusing image 1100 (FIG. 11). The designations “encoded focusing image”and “encoded focusing hologram” are used interchangeably herein.

Referring now to FIG. 12, in step 1210 Applicants' method provides areference focusing image, such as for example reference focusing image828 which is stored in memory 763 (FIG. 7). In certain embodiments,reference focusing image 828 comprises focusing image 1000 (FIG. 10). Incertain embodiments, reference focusing image 828 comprises focusingimage 1100 (FIG. 11).

In step 1220, Applicants' method determines if the holographic datastorage medium comprises a holographically-encoded,computer-generated-focusing image. In certain embodiments, step 1220 isperformed by a storage controller, such as storage controller 760 (FIG.7). If Applicants' method determines in step 1220 that the holographicdata storage medium comprises a holographically-encoded,computer-generated-focusing image, then the method transitions from step1220 to step 1230 wherein the method selects the aholographically-encoded, computer-generated-focusing image. In certainembodiments, step 1230 is performed by a storage controller, such asstorage controller 760 (FIG. 7). Applicants' method then transitionsfrom step 1230 to step 1305 (FIG. 13).

If Applicants' method determines in step 1220 that the holographic datastorage medium does not comprises a holographically-encoded,computer-generated-focusing image, then the method transitions from step1220 to step 1240 wherein the method determines if the holographic datastorage medium comprises a holographically-encoded,factory-written-focusing hologram. In certain embodiments, step 1240 isperformed by a storage controller, such as storage controller 760 (FIG.7). If Applicants' method determines in step 1240 that the holographicdata storage medium comprises an encoded factory-written-focusing image,then the method transitions from step 1240 to step 1250 wherein themethod selects the a holographically-encoded, factory-written-focusingimage. In certain embodiments, step 1250 is performed by a storagecontroller, such as storage controller 760 (FIG. 7). Applicants' methodtransitions from step 1250 to step 1305 (FIG. 13).

If Applicants' method determines in step 1240 that the holographic datastorage medium does not comprises a holographically-encoded,factory-written-focusing image, then the method transitions from step1240 to step 1260 wherein the method determines if the holographic datastorage medium comprises a holographically-encoded,drive-written-focusing hologram. In certain embodiments, step 1260 isperformed by a storage controller, such as storage controller 760 (FIG.7). If Applicants' method determines in step 1260 that the holographicdata storage medium comprises a holographically-encoded,drive-written-focusing image, then the method transitions from step 1260to step 1270 wherein the method selects the a holographically-encoded,factory-written-focusing image. In certain embodiments, step 1270 isperformed by a storage controller, such as storage controller 760 (FIG.7). Applicants' method transitions from step 1270 to step 1305 (FIG.13). If Applicants' method determines in step 1260 that the holographicdata storage medium does not comprises a holographically-encoded,drive-written-focusing image, then the method transitions from step 1260to step 1280 wherein the method decodes the one or more data holograms.

Referring now to FIG. 13, in step 1305 Applicants' method establishes athreshold focusing metric. Step 1305 further comprises retrieving astored threshold focusing metric, such as stored threshold focusingmetric 826 stored in memory 763 (FIG. 7).

In certain embodiments, the threshold focusing metric of step 1310comprises a threshold bit error rate. In certain embodiments, such athreshold bit error rate comprises the maximum percentage of incorrectbits read.

In other embodiments, threshold focusing metric is calculated using amatched filter correlation g(x,y) between any one offactory-written-focusing-hologram 120 (FIG. 1B),drive-written-focusing-hologram 110 (FIG. 1B), orcomputer-generated-focusing hologram 140, decoded from the holographicmedia 100, and the impulse response h(x,y)=s*(−x,−y) of the referencefocusing image 828 (FIG. 7), as shown in Equation [1], where V(x,y) isthe cross-correlation between g(x,y) for thefactory-written-focusing-hologram 120 (FIG. 1B),drive-written-focusing-hologram 110 (FIG. 1B), orcomputer-generated-focusing hologram 140, and s(x,y) for the referencefocusing image 828 (FIG. 7). Equation [1] comprises a double integral,meaning that the integration is over the X-axis and Y-axis directions ofthe optical sensor array 510, both of these axes are perpendicular tothe Z-axis shown in FIG. 1B. Additionally, ξ is the integration variablealong the X axis, η is the integration variable along the Y axis, bothof which and * denotes a complex conjugate.

V(x,y)=∫∫g(ξ,η)s*(ξ−x,η−y)]dξdη  [1]

Mathematically, V(x,y) is a surface varying along the X-axis and theY-axis, for each (x,y). There is one value of V(x,y) for each detectorelement in optical sensor array 510. The range of V(x,y) for each (x,y)is between −1 and +1, where +1 represents the ideal correlation of onehundred (100%). To maximize V(x,y), the following difference surface,Difference(x,y), is defined in Equation. [2]. As shown, Difference(x,y)is calculated by subtracting the matched filter correlation V(x,y) fromunity.

Difference(x,y)=1−V(x,y)  [2]

Difference(x,y) may be evaluated (a) point-to-point, (b) as anarithmetic mean, (c) as a geometric mean, and (d) as a root-mean-square.Difference(x,y) ranges between 0 and +2, and the ideal difference foreach value of (x,y) is 0, meaning for a value of 0 that there is nodifference at that point (x,y) between thefactory-written-focusing-hologram 120 (FIG. 1B),drive-written-focusing-hologram 110 (FIG. 1B), orcomputer-generated-focusing hologram 140, decoded from the holographicmedia 100, and the reference focusing image 828 (FIG. 7).Difference(x,y) may be evaluated point-by-point in thresholdcalculations, but it may be advantageous to quantify surfaceDifference(x,y) in terms of a single number, to simply thresholdcalculations.

Such single numbers may be MAX_Difference which is equal to the maximumvalue of Difference(x,y). Alternately AM_Difference, the arithmetic meanof the values of Difference(x,y), GM_Difference, the geometric mean ofthe values of Difference(x,y), or RMS_Difference, the root-mean-squareof the values of Difference(x,y) may be used in the read differencecalculations.

In certain embodiments, the threshold focusing metric comprises amaximum percentage of incorrectly read characters. For example andreferring to FIG. 10, focusing image 1000 comprises 14 lines of data,wherein each line comprises 36 datapoints. Focusing image 1000 comprises504 characters. In these embodiments, a 99 percent threshold focusingmetric means that 499 of the 504 characters must be correctly read.Referring now to FIG. 11, focusing image 1100 comprises 8 rows, whereineach row comprises 8 objects, for a total of 64 objects. In theseembodiments, a 99 percent focusing metric means that 63 of those 64objects must be correctly read.

Referring FIGS. 8, 9, and 13, in step 1310 Applicants' method positionsthe rotatable imaging lens, such as rotatable imaging lens 850, at an(i)th orientation, wherein index (i) is initially set to 1. In certainembodiments, step 1310 is performed by a storage controller, such asstorage controller 760 (FIG. 7).

In step 1320, Applicants' method illuminates the selected encodedfocusing hologram with a reference beam thereby generating the (i)threconstructed focusing image. In certain embodiments, step 1320 isperformed by a storage controller, such as storage controller 760 (FIG.7).

In step 1330, Applicants' method projects the (i)th reconstructedfocusing image through, inter alia, Applicants' rotatable imaging lensand onto an optical detector array. In step 1340, Applicants' methodcalculates an (i)th measured focusing metric. In certain embodiments,step 1340 is performed by a storage controller, such as storagecontroller 760 (FIG. 7).

In certain embodiments, step 1340 comprises retrieving a referencefocusing image, such as reference focusing image 828 (FIG. 7), andcalculating V(x,y) using Equation [1] for each detector array elementusing the focused, astigmatism-reduced, reconstructed focusing image ofstep 1330 and that reference focusing image. In certain embodiments,step 1340 comprises calculating a bit error rate using the projectedreconstructed focusing image of step 1330 and a reference focusingimage. In certain embodiments, step 1340 comprises calculating acharacter error rate.

In step 1350, Applicants' method determines if the (i)th measuredfocusing metric of step 1340 is greater than or equal to the thresholdfocusing metric of step 1305. In certain embodiments, step 1350 isperformed by a storage controller, such as storage controller 760 (FIG.7).

If Applicants' method determines in step 1350 that the (i)th measuredfocusing metric of step 1340 is greater than or equal to the thresholdfocusing metric of step 1305, then the method transitions from step 1350to step 1355 wherein the method decodes the one or more data hologramsencoded in the holographic data storage medium.

Alternatively, if Applicants' method determines in step 1350 that the(i)th measured focusing metric of step 1340 is not greater than or equalto the threshold focusing metric of step 1305, then the methodtransitions from step 1350 to step 1360 wherein the method rotates therotatable imaging lens in a first direction. In certain embodiments,step 1360 is performed by a storage controller, such as storagecontroller 760 (FIG. 7).

In step 1370 Applicants' method increments (i) by unity. In certainembodiments, step 1370 is performed by a storage controller, such asstorage controller 760 (FIG. 7). In step 1375, Applicants' methodilluminates the selected encoded focusing hologram with a reference beamthereby generating the (i)th reconstructed focusing image. In certainembodiments, step 1375 is performed by a storage controller, such asstorage controller 760 (FIG. 7).

In step 1380, Applicants' method projects the (i)th reconstructedfocusing image through Applicants' rotatably imaging lens and onto anoptical detector array. In step 1385, Applicants' method calculates an(i)th measured focusing metric. In certain embodiments, step 1385 isperformed by a storage controller, such as storage controller 760 (FIG.7).

In certain embodiments, step 1385 comprises retrieving a referencefocusing image, such as reference focusing image 828 (FIG. 7), andcalculating V(x,y) using Equation [1] for each detector array elementusing the focused, astigmatism-reduced, reconstructed focusing image ofstep 1375 and that reference focusing image.

In step 1390, Applicants' method determines if the (i)th measuredfocusing metric of step 1380 is greater than or equal to the (i−1)thmeasured focusing metric of step 1340. In certain embodiments, step 1390is performed by a storage controller, such as storage controller 760(FIG. 7).

If Applicants' method determines in step 1390 that the (i)th measuredfocusing metric of step 1380 is greater than or equal to the (i−1)thmeasured focusing metric of step 1340, then the method transitions fromstep 1390 to step 1510 (FIG. 15). Alternatively, if Applicants' methoddetermines in step 1390 that the (i)th measured focusing metric of step1380 is not greater than or equal to the (i−1)th measured focusingmetric of step 1340, then the method transitions from step 1390 to step1410 (FIG. 14).

Referring now to FIG. 14, in step 1410, Applicants' method returns therotatable imaging lens to the orientation of step 1310 (FIG. 13). Incertain embodiments, step 1410 is performed by a storage controller,such as storage controller 760 (FIG. 7).

In step 1420, Applicants' method rotates the imaging lens in a seconddirection. By “second direction,” Applicants mean the direction oppositethat the direction of step 1360. For example, if the imaging lens wasrotated in a clockwise direction in step 1360, then in step 1420Applicants' method rotates the imaging lens in the counter clockwisedirection. In certain embodiments, step 1420 is performed by a storagecontroller, such as storage controller 760 (FIG. 7).

In step 1430, Applicants' method increments (i) by unity. In certainembodiments, step 1430 is performed by a storage controller, such asstorage controller 760 (FIG. 7). In step 1440, Applicants' methodilluminates the selected encoded focusing hologram with a reference beamthereby generating the (i)th reconstructed focusing image. In certainembodiments, step 1440 is performed by a storage controller, such asstorage controller 760 (FIG. 7).

In step 1450, Applicants' method projects the (i)th reconstructedfocusing image through Applicants' rotatably imaging lens and onto anoptical detector array. In step 1460, Applicants' method calculates an(i)th measured focusing metric, as described herein. In certainembodiments, step 1460 is performed by a storage controller, such asstorage controller 760 (FIG. 7).

In step 1470, Applicants' method determines if the (i)th measuredfocusing metric of step 1460 is greater than or equal to the measuredfocusing metric of step 1385. In certain embodiments, step 1470 isperformed by a storage controller, such as storage controller 760 (FIG.7).

If Applicants' method determines in step 1470 that the (i)th measuredfocusing metric of step 1460 is not greater than or equal to themeasured focusing metric of step 1385, then the method transitions fromstep 1470 to step 1480 wherein the method returns the imaging lens tothe orientation of step 1410, as that orientation gives the bestfocusing metric. In certain embodiments, step 1480 is performed by astorage controller, such as storage controller 760 (FIG. 7).

In step 1490, Applicants' method decodes the one or more encoded dataholograms. In certain embodiments, step 1490 is performed by a storagecontroller, such as storage controller 760 (FIG. 7). If Applicants'method determines in step 1470 that the (i)th measured focusing metricof step 1460 is greater than or equal to the measured focusing metric ofstep 1385, then the method transitions from step 1470 to step 1510 (FIG.15).

Referring now to FIG. 15, in step 1510 Applicants' method determines ifthe (i)th measured focusing metric of step 1460 is greater than or equalto the threshold focusing metric of step 1305 (FIG. 13). In certainembodiments, step 1510 is performed by a storage controller, such asstorage controller 760 (FIG. 7).

If Applicants' method determines in step 1510 that the (i)th measuredfocusing metric of step 1460 is greater than or equal to the thresholdfocusing metric of step 1305, then the method transitions from step 1510to step 1590 wherein the method decodes the one or more data holograms.In certain embodiments, step 1590 is performed by a storage controller,such as storage controller 760 (FIG. 7).

Alternatively, if Applicants' method determines in step 1510 that the(i)th measured focusing metric of step 1460 is not greater than or equalto the threshold focusing metric of step 1305, then the methodtransitions from step 1510 to step 1520 wherein the method rotates theimaging lens in the selected direction of step 1360 (FIG. 13) if themethod transitioned from step 1390 to step 1510, or in the selecteddirection of step 1420 (FIG. 14) if the method transitioned from step1470 to step 1510. In certain embodiments, step 1520 is performed by astorage controller, such as storage controller 760 (FIG. 7).

In step 1530, Applicants' method increments (i) by unity. In certainembodiments, step 1530 is performed by a storage controller, such asstorage controller 760 (FIG. 7). In step 1540, Applicants' methodilluminates the selected encoded focusing hologram with a reference beamthereby generating the (i)th reconstructed focusing image. In certainembodiments, step 1540 is performed by a storage controller, such asstorage controller 760 (FIG. 7).

In step 1550, Applicants' method projects the (i)th reconstructedfocusing image through Applicants' rotatably imaging lens and onto anoptical detector array. In step 1560, Applicants' method calculates an(i)th measured focusing metric, as described herein. In certainembodiments, step 1560 is performed by a storage controller, such asstorage controller 760 (FIG. 7).

In step 1570, Applicants' method determines if the (i)th measuredfocusing metric of step 1560 is greater than or equal to the measuredfocusing metric of step 1460. In certain embodiments, step 1570 isperformed by a storage controller, such as storage controller 760 (FIG.7).

If Applicants' method determines in step 1570 that the (i)th measuredfocusing metric of step 1570 is greater than or equal to the measuredfocusing metric of step 1460, then the method transitions from step 1570to step 1510 and continues as described herein.

If Applicants' method determines in step 1570 that the (i)th measuredfocusing metric of step 1570 is not greater than or equal to themeasured focusing metric of step 1460, then the method transitions fromstep 1570 to step 1580 wherein the method returns the rotatable imaginglens to the (i−1)th orientation. In certain embodiments, step 1580 isperformed by a storage controller, such as storage controller 760 (FIG.7). Applicants' method transitions from step 1580 to step 1590 whereinthe method decodes the one or more data holograms encoded in theholographic data storage medium.

In certain embodiments, individual steps recited in FIG. 12, 13, 14,and/or 15, may be combined, eliminated, or reordered.

In certain embodiments, Applicants' invention includes instructions,such as instructions 824 (FIG. 7), residing in memory 763 (FIG. 7),where those instructions are executed by a processor, such as processor764 (FIG. 7), to perform one or more of steps 1220, 1230, 1240, 1250,1260, 1270, and/or 1280, recited in FIG. 12, and/or one or more of steps1305, 1310, 1320, 1330, 1340, 1350, 1355, 1360, 1370, 1375, 1380, 1385,and/or 1390, recited in FIG. 13, and/or one or more to steps 1410, 1420,1430, 1440, 1450, 1460, 1470, 1480, and/or 1490, recited in FIG. 14,and/or one or more of steps 1510, 1520, 1530, 1540, 1550, 1560, 1570,1580, and/or 1590, recited in FIG. 15.

In certain embodiments, Applicants' invention includes instructionsresiding in any other computer program product, where those instructionsare executed by a computer external to, or internal to, holographic datastorage system 200, holographic data storage system 300, and/orholographic data storage and retrieval system 700, to perform one ormore of steps 1220, 1230, 1240, 1250, 1260, 1270, and/or 1280, recitedin FIG. 12, and/or one or more of steps 1305, 1310, 1320, 1330, 1340,1350, 1355, 1360, 1370, 1375, 1380, 1385, and/or 1390, recited in FIG.13, and/or one or more to steps 1410, 1420, 1430, 1440, 1450, 1460,1470, 1480, and/or 1490, recited in FIG. 14, and/or one or more of steps1510, 1520, 1530, 1540, 1550, 1560, 1570, 1580, and/or 1590, recited inFIG. 15.

In either case, the instructions may be encoded in an informationstorage medium comprising, for example, a magnetic information storagemedium, an optical information storage medium, an electronic informationstorage medium, and the like. By “electronic storage media,” Applicantsmean, for example, a device such as a PROM, EPROM, EEPROM, Flash PROM,compactflash, smartmedia, and the like.

While the preferred embodiments of the present invention have beenillustrated in detail, it should be apparent that modifications andadaptations to those embodiments may occur to one skilled in the artwithout departing from the scope of the present invention as set forthin the following claims.

1. A method to store information in a holographic data storage medium,comprising the steps of: supplying a holographic data storage mediumcomprising an encoded focusing hologram and one or more encoded dataholograms; providing a first holographic data storage system comprisinga light source, an optical detector array and a rotatable imaging lens;disposing said holographic data storage medium in said holographic datastorage system; disposing said rotatable imaging lens at an (i)thorientation, wherein (i) is initially set to 1; establishing a thresholdfocusing metric; illuminating said encoded focusing hologram with areference beam to generate an (i)th reconstructed focusing image;projecting said (i)th reconstructed focusing image through saidrotatable imaging lens, and onto said optical detector array;calculating an (i)th measured focusing metric; determining if said (i)thmeasured focusing metric is greater than or equal to said thresholdfocusing metric; operative if said (i)th measured focusing metric isgreater than or equal to said threshold focusing metric, decoding saidone or more encoded data holograms.
 2. The method of claim 1, whereinsaid providing a first holographic data storage system further comprisesproviding a first holographic data storage system comprising a servocomprising a rotatable shaft extending outwardly therefrom, wherein saidrotatable shaft comprises a spiral-threaded portion, and wherein saidrotatable imaging lens comprises a periphery and a plurality of gearteeth disposed along said periphery, and wherein one or more of saidplurality of gear teeth are intermeshed with said spiral-threadedportion.
 3. The method of claim 1, wherein said supplying step furthercomprises the steps of: providing a computer-generated-hologramcomprising a focusing image; disposing said computer-generated-holograminto said holographic data storage medium at the time of manufacture. 4.The method of claim 1, wherein said supplying step further comprises thesteps of: providing a focusing image; encoding said focusing image intosaid holographic data storage medium at the time of manufacture.
 5. Themethod of claim 1, wherein said supplying step further comprises thesteps of: providing a second holographic data storage system; providinga holographic data storage medium; disposing said holographic datastorage medium in said second holographic data storage system; providinga focusing image; providing information; generating a focusing hologramcomprising said focusing image, and one or more data holograms, whereineach of said one or more data holograms comprises an image of all or aportion of said information; encoding said focusing hologram and saidone or more data holograms into said holographic data storage medium. 6.The method of claim 1, further comprising the steps of: determining ifsaid holographic data storage medium comprises acomputer-generated-focusing hologram; operative if said holographic datastorage medium comprises a computer-generated-focusing hologram,selecting said computer-generated-focusing hologram; operative if saidholographic data storage medium does not comprise acomputer-generated-focusing hologram, determining if said holographicdata storage medium comprises a factory-written-focusing hologram;operative if said holographic data storage medium comprises afactory-written-focusing hologram, selecting saidfactory-written-focusing hologram; operative if said holographic datastorage medium does not comprise a factory-written-focusing hologram,determining if said holographic data storage medium comprises adrive-written-focusing hologram; operative if said holographic datastorage medium comprises a drive-written-focusing hologram, selectingsaid drive-written-focusing hologram; wherein said illuminating stepfurther comprises illuminating said selected focusing hologram.
 7. Themethod of claim 1, further comprising the steps of: operative if said(i)th measured focusing metric is not greater than or equal to saidthreshold focusing metric, incrementing (i) by unity; rotating saidrotatable imaging lens in a first direction to an (i)th orientation;illuminating said encoded focusing image with a reference beam togenerate an (i)th reconstructed focusing image; projecting said (i)threconstructed focusing image through said rotatable imaging lens, andonto said optical detector array; calculating an (i)th measured focusingmetric; determining if said (i)th measured focusing metric is greaterthan or equal to said threshold focusing metric; operative if said (i)thmeasured focusing metric is greater than or equal to said thresholdfocusing metric, decoding said one or more encoded data holograms. 8.The method of claim 7, further comprising the steps of: operative ifsaid (i)th measured focusing metric is not greater than or equal to saidthreshold focusing metric, determining if said (i)th measured focusingmetric is greater than said (i−1)th focusing metric; operative if said(i)th measured focusing metric is greater than said (i−1)th focusingmetric, repeating the steps of claim
 7. 9. The method of claim 8,further comprising the steps of: operative if said (i)th measuredfocusing metric is not greater than said (i−1)th focusing metric,returning said rotatable imaging lens to an (i−1)th orientation;incrementing (i) by unity; rotating said rotatable imaging lens in asecond direction to the (i)th orientation, wherein said second directionis opposite to said first direction; illuminating said encoded focusingimage with a reference beam to generate an (i)th reconstructed focusingimage; projecting said (i)th reconstructed focusing image through saidrotatable imaging lens, and onto said optical detector array;calculating an (i)th measured focusing metric; determining if said (i)thmeasured focusing metric is greater than or equal to said thresholdfocusing metric; operative if said (i)th measured focusing metric isgreater than or equal to said threshold focusing metric, decoding saidone or more encoded data holograms.
 10. A storage controller comprisinga processor and computer readable program code disposed in a computerreadable medium, wherein said storage controller is in communicationwith a holographic data storage system comprising a lasing device, anoptical detector array, a rotatable imaging lens, and a holographic datastorage medium comprising an encoded focusing image and one or moreencoded data holograms, said computer readable program code beinguseable with said processor to store information in said holographicdata storage medium, the computer readable program code comprising aseries of computer readable program steps to effect: disposing saidrotatable imaging lens at an (i)th orientation, wherein (i) is initiallyset to 1; retrieving a threshold focusing metric; illuminating saidencoded focusing image with a reference beam to generate an (i)threconstructed focusing image, wherein said (i)th reconstructed focusingimage is projected through said rotatable imaging lens and onto saidoptical detector array; calculating an (i)th measured focusing metric;determining if said (i)th measured focusing metric is greater than orequal to said threshold focusing metric; operative if said (i)thmeasured focusing metric is greater than or equal to said thresholdfocusing metric, decoding said one or more encoded data holograms. 11.The storage controller of claim 10, wherein said holographic datastorage system further comprises a servo comprising a rotatable shaftextending outwardly therefrom, wherein said rotatable shaft comprises aspiral-threaded portion, and wherein said rotatable imaging lenscomprises a periphery and a plurality of gear teeth disposed along saidperiphery, and wherein one or more of said plurality of gear teeth areintermeshed with said spiral-threaded portion.
 12. The storagecontroller of claim 10, said computer readable program code furthercomprising a series of computer readable program steps to effect:determining if said holographic data storage medium comprises acomputer-generated-focusing hologram; operative if said holographic datastorage medium comprises a computer-generated-focusing hologram,selecting said computer-generated-focusing hologram; operative if saidholographic data storage medium does not comprise acomputer-generated-focusing hologram, determining if said holographicdata storage medium comprises a factory-written-focusing hologram;operative if said holographic data storage medium comprises afactory-written-focusing hologram, selecting saidfactory-written-focusing hologram; operative if said holographic datastorage medium does not comprise a factory-written-focusing hologram,determining if said holographic data storage medium comprises adrive-written-focusing hologram; operative if said holographic datastorage medium comprises a drive-written-focusing hologram, selectingsaid drive-written-focusing hologram; wherein said illuminating stepfurther comprises illuminating said selected focusing hologram.
 13. Thestorage controller of claim 12, said computer readable program codefurther comprising a series of computer readable program steps toeffect: operative if said (i)th measured focusing metric is not greaterthan or equal to said threshold focusing metric, rotating said rotatableimaging lens in a first direction; incrementing (i) by unity;illuminating said encoded focusing image with a reference beam togenerate an (i)th reconstructed focusing image, wherein said (i)threconstructed focusing image is projected through said rotatable imaginglens and onto said optical detector array; calculating an (i)th measuredfocusing metric; determining if said (i)th measured focusing metric isgreater than or equal to said threshold focusing metric; operative ifsaid (i)th measured focusing metric is greater than or equal to saidthreshold focusing metric, decoding said one or more encoded dataholograms.
 14. The storage controller of claim 13, said computerreadable program code further comprising a series of computer readableprogram steps to effect: operative if said (i)th measured focusingmetric is not greater than or equal to said threshold focusing metric,determining if said (i)th measured focusing metric is greater than said(i−1)th focusing metric; operative if said (i)th measured focusingmetric is greater than said (i−1)th focusing metric, rotating saidrotatable imaging lens in said first direction; incrementing (i) byunity; illuminating said encoded focusing image with a reference beam togenerate an (i)th reconstructed focusing image, wherein said (i)threconstructed focusing image is projected through said rotatable imaginglens and onto said optical detector array; calculating an (i)th measuredfocusing metric; determining if said (i)th measured focusing metric isgreater than or equal to said threshold focusing metric; operative ifsaid (i)th measured focusing metric is greater than or equal to saidthreshold focusing metric, decoding said one or more encoded dataholograms.
 15. The storage controller of claim 14, further comprisingthe steps of: operative if said (i)th measured focusing metric is notgreater than said (i−1)th focusing metric, returning said rotatableimaging lens to the (i−1)th orientation; incrementing (i) by unity;rotating said rotatable imaging lens in a second direction to the (i)thorientation, wherein said second direction is opposite to said firstdirection; illuminating said encoded focusing image with a referencebeam to generate an (i)th reconstructed focusing image, wherein said(i)th reconstructed focusing image is projected through said rotatableimaging lens and onto said optical detector array; calculating an (i)thmeasured focusing metric; determining if said (i)th measured focusingmetric is greater than or equal to said threshold focusing metric;operative if said (i)th measured focusing metric is greater than orequal to said threshold focusing metric, decoding said one or moreencoded data holograms.
 16. A computer program product encoded in acomputer readable medium disposed in a holographic data storage systemcomprising a processor, a lasing device, an optical detector array, arotatable imaging lens, and a holographic data storage medium comprisingan encoded focusing image and one or more encoded data holograms, saidcomputer program product being useable with said processor to encodeinformation in said holographic data storage medium, comprising:computer readable program code which causes said programmable computerprocessor to dispose said rotatable imaging lens at an (i)thorientation, wherein (i) is initially set to 1; computer readableprogram code which causes said programmable computer processor toretrieve a threshold focusing metric; computer readable program codewhich causes said programmable computer processor to illuminate saidencoded focusing image with a reference beam to generate an (i)threconstructed focusing image, wherein said (i)th reconstructed focusingimage is projected through said rotatable imaging lens and onto saidoptical detector array; computer readable program code which causes saidprogrammable computer processor to calculate an (i)th measured focusingmetric; computer readable program code which causes said programmablecomputer processor to determine if said (i)th measured focusing metricis greater than or equal to said threshold focusing metric; computerreadable program code which, if said (i)th measured focusing metric isgreater than or equal to said threshold focusing metric, causes saidprogrammable computer processor to decode said one or more encoded dataholograms.
 17. The computer program product of claim 16, furthercomprising: computer readable program code which causes saidprogrammable computer processor to determine if said holographic datastorage medium comprises a computer-generated-focusing hologram;computer readable program code, which, if said holographic data storagemedium comprises a computer-generated-focusing hologram, causes saidprogrammable computer processor to select saidcomputer-generated-focusing hologram; computer readable program codewhich, if said holographic data storage medium does not comprise acomputer-generated-focusing hologram, causes said programmable computerprocessor to determine if said holographic data storage medium comprisesa factory-written-focusing hologram; computer readable program codewhich, if said holographic data storage medium comprises afactory-written-focusing hologram, causes said programmable computerprocessor to select said factory-written-focusing hologram; computerreadable program code which, if said holographic data storage mediumdoes not comprise a factory-written-focusing hologram, causes saidprogrammable computer processor to determine if said holographic datastorage medium comprises a drive-written-focusing hologram; computerreadable program code which, if said holographic data storage mediumcomprises a drive-written-focusing hologram, causes said programmablecomputer processor to select said drive-written-focusing hologram;wherein said computer readable program code which causes saidprogrammable computer processor to illuminate an encoded focusing imagefurther comprises computer readable program code which causes saidprogrammable computer processor to illuminate said selected focusinghologram.
 18. The computer program product of claim 16, furthercomprising the steps of: computer readable program code which, if said(i)th measured focusing metric is not greater than or equal to saidthreshold focusing metric, causes said programmable computer processorto rotate said rotatable imaging lens in a first direction; computerreadable program code which causes said programmable computer processorto increment (i) by unity; computer readable program code which causessaid programmable computer processor to illuminate said encoded focusingimage with a reference beam to generate an (i)th reconstructed focusingimage, wherein said (i)th reconstructed focusing image is projectedthrough said rotatable imaging lens and onto said optical detectorarray; computer readable program code which causes said programmablecomputer processor to calculate an (i)th measured focusing metric;computer readable program code which causes said programmable computerprocessor to determine if said (i)th measured focusing metric is greaterthan or equal to said threshold focusing metric; computer readableprogram code which, if said (i)th measured focusing metric is greaterthan or equal to said threshold focusing metric, causes saidprogrammable computer processor to decode said one or more encoded dataholograms.
 19. The computer program product of claim 18, furthercomprising the steps of: computer readable program code which, if said(i)th measured focusing metric is not greater than or equal to saidthreshold focusing metric, causes said programmable computer processorto determine if said (i)th measured focusing metric is greater than said(i−1)th focusing metric; computer readable program code which, if said(i)th measured focusing metric is greater than said (i−1)th focusingmetric, causes said programmable computer processor to rotate saidrotatable imaging lens in said first direction; computer readableprogram code which causes said programmable computer processor toincrement (i) by unity; computer readable program code which causes saidprogrammable computer processor to illuminate said encoded focusingimage with a reference beam to generate an (i)th reconstructed focusingimage, wherein said (i)th reconstructed focusing image is projectedthrough said rotatable imaging lens and onto said optical detectorarray; computer readable program code which causes said programmablecomputer processor to calculate an (i)th measured focusing metric;computer readable program code which causes said programmable computerprocessor to determine if said (i)th measured focusing metric is greaterthan or equal to said threshold focusing metric; computer readableprogram code which, if said (i)th measured focusing metric is greaterthan or equal to said threshold focusing metric, causes saidprogrammable computer processor to decode said one or more encoded dataholograms.
 20. The computer program product of claim 19, furthercomprising the steps of: computer readable program code which, if said(i)th measured focusing metric is not greater than said (i−1)th focusingmetric, causes said programmable computer processor to dispose saidrotatable imaging lens at the (i−1)th orientation; computer readableprogram code which causes said programmable computer processor toincrement (i) by unity; computer readable program code which causes saidprogrammable computer processor to rotate said rotatable imaging lens ina second direction to the (i)th orientation, wherein said seconddirection is opposite to said first direction; computer readable programcode which causes said programmable computer processor to illuminatesaid encoded focusing image with a reference beam to generate an (i)threconstructed focusing image, wherein said (i)th reconstructed focusingimage is projected through said rotatable imaging lens and onto saidoptical detector array; computer readable program code which causes saidprogrammable computer processor to calculate an (i)th measured focusingmetric; computer readable program code which causes said programmablecomputer processor to determine if said (i)th measured focusing metricis greater than or equal to said threshold focusing metric; computerreadable program code which, if said (i)th measured focusing metric isgreater than or equal to said threshold focusing metric, causes saidprogrammable computer processor to decode said one or more encoded dataholograms.